The subject matter disclosed herein relates generally to propulsion systems, and in particular to a propulsion system for a rotary wing aircraft having improved efficiency.
Existing rotary wing aircraft (e.g., intermediate to medium-weight class rotorcraft) utilize propulsion systems to power aircraft flight, that may include spark ignition (SI) or compression ignition (CI) engines. Energy (stored in chemical form as fuel) is supplied to an energy conversion device (a gas turbine engine) and is transmitted through a transmission mechanism (the main rotor gearbox), from which mechanical work (in the form of shaft power supplied to drive the main rotor and tail rotor) and heat emerge. One exemplary aircraft is an S-76 helicopter. During steady, level flight the conventional propulsion system of the S-76 converts only a small portion of the chemical energy stored in the Jet-A fuel (⅓) to mechanical energy. The remainder of the energy is lost to the surrounding environment in the form of heat (⅔), primarily through high-temperature exhaust and cooling air. System accessories (such as the aircraft's electrical load requirements) and mechanical transmission losses contribute an additional 1-2% energy loss in the system, resulting in even lower useful shaft power to the main and tail rotors. A propulsion system for a rotary wing aircraft having higher efficiency would be well received in the art.